The present invention relates to vibration isolation and, more particularly, to vibration isolation in applications requiring stable, high-precision, location of a workpiece with respect to an apparatus.
One type of apparatus capable of benefitting from the present invention includes a positioning table employed to position a workpiece with respect to an apparatus performing a desired function on the workpiece. Positioning tables are in routine use in applications wherein a workpiece is positioned along a linear axis for performing work thereon. Such a positioning table may be part of a system employing two or three stacked tables controllable along mutually orthogonal axes.
Some positioning tables are employed in applications requiring such precise and stable positioning that the required precision may be destroyed by vibration transmitted to the positioning table through the support structure of the apparatus. Such degradation in precision is especially severe when the frequencies of vibrations applied to the structure are capable of exciting resonant frequencies of the structure.
The prior art employs deep foundation structures isolated as much as possible from the surrounding earth to impart as much stability as possible to the base of a positioning table. Other techniques employ massive granite bases for damping higher vibration frequencies to prevent their transmission to a workpiece mounted on the positioning table.
In addition, relative motion between a workpiece and an apparatus performing a function on it may occur due to differences in resonant frequency, or amplitudes of vibrational motion of the two elements.
When relative positioning stability on the order of nanometers is required between a workpiece and, for example, a charged-particle-beam device of a type used for processing semiconductor masks or wafers, prior-art techniques fail to provide adequate solutions.